Viscoelastic materials may be designed to possess a wide variety of chemical and physical properties. As a result, viscoelastic materials may be useful for constructing a wide variety of articles for a wide variety of uses. The versatility of viscoelastic articles presents certain manufacturing challenges for the construction of such articles, particularly in a commercial setting where cost effective, large-scale manufacturing is particularly desirable. Speed and consistency of manufacture and reduction of waste are all issues of specific concern for any commercial manufacturing process.
Articles including viscoelastic materials, e.g., pressure sensitive adhesive (PSA) materials, may be manufactured using a variety of processes. For example, transfer tapes including segmented PSAs may be constructed using a carrier web embossed to contain recesses in a surface of the web. The recesses of the web may be coated with a release coating. A curable composition (e.g., a composition that may be cured to form a PSA) is coated into the recesses of the web over the release coating. A cover sheet, e.g. a film constructed of polyethylene terephthalate (“PET”), is coated over the curable composition and the web/composition/cover sheet assembly is exposed to UV irradiation to cure the composition into the PSA. The entire assembly is wound into a roll. When the assembly is unrolled, the PSA adheres to the film cover sheet and releases from the recesses of the web, thereby forming a film coated with a segmented PSA in the pattern provided by the recesses on the surface of the web. This process may be undesirable for manufacturing certain viscoelastic articles on a commercial scale because the web is not reusable, thereby creating waste, and the process cannot be practiced on a continuous basis. The process must be periodically interrupted to provide a fresh supply of the web material.
In another example, PSA-coated articles such as adhesive tapes and transfer coatings may be constructed by extruding a coating of PSA onto a molding tool. The surface of the PSA coating that is not in contact with the molding tool is contacted with a substrate, thereby transferring the PSA to the substrate. The PSA of the resulting article bears the surface structure provided by the molding tool. To ensure clean separation of the PSA layer from the structured surface of the molding tool, the adhesion of the PSA to the substrate must be greater than the adhesion of the PSA to the surface of the molding tool. This process is limited to manufacturing viscoelastic articles that can be constructed from extrudable viscoelastic materials. Also, this process does not provide a method of manufacturing a self-supporting viscoelastic article, i.e., a viscoelastic article that may exist independent of the substrate used to remove the adhesive layer from the molding tool.
A PSA transfer coating may be constructed that is independent of any backing layer by coating a PSA layer onto a release liner. The coated liner may then be rolled upon itself, thereby embossing the PSA layer with any structure that may be provided on one or both surfaces of the release liner. The transfer coating subsequently may be removed from the release liner, providing a transfer coating that is independent of any sort of backing layer. This process cannot be practiced on a continuous basis because the process must be periodically interrupted to provide a new supply of the release liner. Also, this process is limited to manufacturing viscoelastic articles that can be constructed from extrudable and embossible viscoelastic materials.
It may be desirable to manufacture viscoelastic articles from curable compositions on a continuous basis. It may further be desirable to manufacture viscoelastic articles on a continuous basis that are independent of a backing material. Present processes for manufacturing viscoelastic materials from curable compositions cannot be performed on a continuous basis and do not permit the continuous manufacturing of viscoelastic articles independent of a backing layer.
A need exists for a continuous method of manufacturing viscoelastic articles from curable compositions, including the continuous manufacturing of viscoelastic articles that are independent of a backing layer.